565. Array Nesting(dfs 血的教训)

为什么说是血的教训呢，因为明明自己想的思路与那些AC的人思路一样

而自己偏偏超时，又爆内存，觉得很奇怪，偏偏又找不出问题所在

这道题，看完题意就知道dfs的思路了，却因为很小的细节卡了我2个小时！！！！！ 泪崩

先看题目：

A zero-indexed array A consisting of N different integers is given. The array contains all integers in the range [0, N - 1].

Sets S[K] for 0 <= K < N are defined as follows:

S[K] = { A[K], A[A[K]], A[A[A[K]]], ... }.

Sets S[K] are finite for each K and should NOT contain duplicates.

Write a function that given an array A consisting of N integers, return the size of the largest set S[K] for this array.

Example 1:

Input: A = [5,4,0,3,1,6,2]
Output: 4
Explanation: 
A[0] = 5, A[1] = 4, A[2] = 0, A[3] = 3, A[4] = 1, A[5] = 6, A[6] = 2.

One of the longest S[K]:
S[0] = {A[0], A[5], A[